Method for patterning semiconductor devices on a silicon substrate using oxynitride film

ABSTRACT

A method for fabricating and patterning semiconductor devices with a resolution down to 0.12 μm on a substrate structure. The method begins by providing a substrate structure comprising various layers of oxide and/or nitride formed over either monocrystalline silicon or polycrystalline silicon. A silicon oxynitride layer is formed on the substrate structure. Key characteristics of the oxynitride layer include: a refractive index of between about 1.85 and 2.35 at a wavelength of 248 nm, an extinction coefficient of between 0.45 and 0.75 at a wavelength of 248 nm, and a thickness of between about 130 Angstroms and 850 Angstroms. A photoresist layer is formed over the silicon oxynitride layer and exposed at a wavelength of between about 245 nm and 250 nm; whereby during exposure at a wavelength of between 245 nm 250 nm, the silicon oxynitride layer provides a phase-cancel effect.

BACKGROUND OF INVENTION

[0001] 1) Field of the Invention

[0002] This invention relates generally to fabrication of semiconductordevices and more particularly to patterning semiconductor devices withresolution down to 0.12 μm on a silicon substrate using oxynitride film.

[0003] 2) Description of the Prior Art

[0004] The semiconductor industry's continuing drive towardsemiconductor devices with ever decreasing geometries coupled with thereflective property of monocrystalline silicon and polycrystallinesilicon (polysilicon, poly) have led to increasing photolithographicpatterning problems. Unwanted reflections from the underlyingmonocrystalline silicon or polycrystalline silicon during thephotolithographic patterning process cause the resulting photoresistpatterns to be distorted. Diffraction of the light waves used to exposethe photoresist during patterning also causes distortion of theresulting patterns.

[0005] Organic and inorganic bottom anti-reflective coatings have beenattempted on both monocrystalline silicon and polycrystalline silicon toabsorb reflected energy and prevent pattern distortion. However,different film thicknesses due to surface topography after coating willcause etching issues, photoresist loss and poor after etch inspection(AEI) dimensions.

[0006] Phase-shifting masks have been used to compensate for diffractionand enhance the resolution of photolithographic patterns. A phase shiftlayer is used to cover one of a pair of adjacent apertures of thepattern mask during exposure. The phase shifting layer reverses the signof the electric field of its aperture. The distortions of the electricfield from adjacent appertures caused by diffraction cancel because theyhave opposite signs. The phase change is a function of wavelength andthickness of the transparent phase shifting layer. However, phaseshifting masks do not prevent distortion from reflections.

[0007] The importance of overcoming the various deficiencies noted aboveis evidenced by the extensive technological development directed to thesubject, as documented by the relevant patent and technical literature.The closest and apparently more relevant technical developments in thepatent literature can be gleaned by considering the following patents.

[0008] U.S. Pat. No. 5,600,165 (Tsukamoto et al.) shows a SiON layer asa bottom ARC over several different structures, including polysilicon,oxide, and suicides.

[0009] U.S. Pat. No. 5,639,687 (Roman et al.) shows a Si-rich SiON ARClayer in which thickness (t) is determined as a function of wavelength(λ) and refractive index (n) using the formula t=λ/4n.

[0010] U.S. Pat. No. 5,252,515 (Tsai et al.) teaches a process forforming SiON ARC layer with refractive index (n) of between 1.5 and 2.1by controlling the silane flow rate.

[0011] U.S. Pat. No. 4,717,631 (Kaganowicz et al.) shows a SiONpassivation layer having a refractive index (n) of between 1.55 and 1.75at a wavelength (λ) of 632.8 nm.

SUMMARY OF THE INVENTION

[0012] It is an object of the present invention to provide a method ofpatterning semiconductor devices on a silicon substrate using oxynitridefilms.

[0013] It is another object of the present invention to provide a methodof patterning semiconductor devices with a resolution down to 0.12 μm onmonocrystalline silicon or polycrystalline silicon.

[0014] It is yet another object of the present invention to provide amethod of patterning semiconductor devices using both patternedstructure and optical properties of oxynitride to acheive resolutiondown to 0.12 μm.

[0015] To accomplish the above objectives, the present inventionprovides a method for fabricating and patterning semiconductor deviceswith a resolution down to 0.12 μm on a substrate structure (10). Themethod begins by providing a substrate structure comprising variouslayers of oxide and/or nitride formed over either monocrystallinesilicon or polycrystalline silicon. A silicon oxynitride layer (16) isformed on the substrate structure (10). Key characteristics of theoxynitride layer include: a refractive index of between about 1.85 and2.35 at a wavelength of 248 nm, an extinction coefficient of between0.45 and 0.75 at a wavelength of 248 nm, and a thickness of betweenabout 130 Angstroms and 850 Angstroms. A photoresist layer (20) isformed over the silicon oxynitride layer (16) and exposed at awavelength of between about 245 nm and 250 nm; whereby during exposureat a wavelength of between 245 nm and 250 nm, the silicon oxynitridelayer (16) provides a phase-cancel effect, and acts as an inorganicanti-reflective coating, absorbing reflected light energy.

[0016] The present invention provides considerable improvement over theprior art. The absorptive properties of the oxynitride layer (20) reducethe amount of reflected energy, thereby reducung pattern distortion. Akey advantage of the present invention is that during exposure, thesilicon oxynitride layer (16) also provides a phase-cancel effect. Thereflected light is out of phase with and cancels the diffracted lightenergy, further reducing pattern distortion.

[0017] The present invention achieves these benefits in the context ofknown process technology. However, a further understanding of the natureand advantages of the present invention may be realized by reference tothe latter portions of the specification and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The features and advantages of a semiconductor device accordingto the present invention and further details of a process of fabricatingsuch a semiconductor device in accordance with the present inventionwill be more clearly understood from the following description taken inconjunction with the accompanying drawings in which like referencenumerals designate similar or corresponding elements, regions andportions and in which:

[0019]FIG. 1 is a sectional view of a device fabricated according thefirst embodiment of the invention.

[0020]FIG. 2 is a sectional view of a device fabricated according thesecond embodiment of the invention.

[0021]FIG. 3 is a sectional view of a device fabricated according thethird embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be described in detail with referenceto the accompanying drawings.

[0023] Substrate structure as used herein means a monocrystallinesilicon structure suitable for manufacturing semiconductor devices whichcan have one or more processing steps already performed thereon. Siliconlayer as used herein means either a monocrystalline layer or apolycrystalline layer formed over a substrate structure unless otherwisestated.

[0024] First Embodiment

[0025] In the first embodiment, a silicon oxynitride layer (16) isformed over a monocrystalline silicon substrate structure (10), an oxidelayer (12) and a nitride layer (14) and patterned with a resolution ofdown to 0.12 μm.

[0026] The process begins by forming an oxide layer (12) on amonocrystalline silicon substrate structure (10). The oxide layer (12)is preferably formed using a LPCVD process. The oxide layer preferablyhas a thickness of between about 50 Angstroms and 300 Angstroms.

[0027] A nitride layer (14) is formed on the oxide layer (12). Thenitride layer is preferably formed using LPCVD and has a thickness ofbetween about 1000 Angstroms and 2500 Angstroms. The nitride layer has arefractive index of between 2.28 and 2.32 and an extinction coefficientof between about 0.015 and 0.025 at a wavelength of 248 nanometers.

[0028] A silicon oxynitride layer (16) is formed on the nitride layer(14). The silicon oxynitride layer (16) has a refractive index ofbetween about 1.85 and 2.35 and an extinction coefficient of between0.45 and 0.75 at a wavelength of 248 nanometers. The silicon oxynitridelayer preferably has a thickness of between about 130 Angstroms and 850Angstroms.

[0029] The silicon oxynitride layer (16) can be formed using a plasmaenhanced chemical vapor deposition (PECVD) process at a temperature ofbetween about 200° C. and 550° C., at a pressure of between about 3 torrand 8 torr, and at a power of between about 120 Watts and 200 Watts. Thesilicon oxynitride layer (16) is preferably formed in a plasmadeposition chamber such as an Applied Materials Centura or PE5000 usingsilane at a flow rate of between about 30 sccm and 80 sccm, nitric oxideat a flow rate of between about 50 sccm and 130 sccm, and helium at aflow rate of between about 1500 sccm and 2500 sccm. It should beunderstood that the flow rates and power can be scaled up or downdepending upon chamber size provided the ratios are maintained.

[0030] A photoresist layer (20) is formed over the silicon oxynitridelayer (16). The photoresist layer (20) has a thickness of between about3000 Angstroms and 8000 Angstroms.

[0031] The photoresist layer (20) is exposed to light energy at awavelength of between about 245 nanometers and 250 nanometers. Theabsorptive properties of the oxynitride layer (20) reduce the amount ofreflected energy, thereby reducung pattern distortion. A key advantageof the present invention is that during exposure, the silicon oxynitridelayer (16) also provides a phase-cancel effect. The reflected light isout of phase with and cancels the diffracted light energy, furtherreducing pattern distortion.

[0032] The photoresist layer (20) is developed to form an opening (25).In a preferred embodiment, the oxynitride layer (16), the nitride layer(14) and the oxide layer (12) are patterned through the opening (25) toform a contact opening.

[0033] Second Embodiment

[0034] In the second embodiment, a silicon oxynitride layer (16) isformed on an oxide layer (12B) overlying a monocrystalline orpolycrystalline silicon layer (11), either with or without a tungstensilicide top layer, and overlying a substrate structure (10), andpatterned with a resolution of down to 0.12 μm.

[0035] The method begins by forming an oxide layer (12B) on a siliconlayer (11) overlying a substrate structure (10). The oxide layer (12B)is preferably composed of a silicon glass such as undoped silicon glass(USG), boron and phosphorous doped silicon glass (BPSG) or phosphorousdoped silicon glass (PSG) as are known in the art. The oxide layer (12B)of the second embodiment preferably has a thickness of between about1000 Angstroms and 5000 Angstroms, a refractive index (n) of betweenabout 1.4 and 1.65, and an extinction coefficient (k) of between about 0and 0.1. The oxide layer (12B) is preferably formed using an O₃— TEOSprocess as is known in the art. In a preferred embodiment, the siliconlayer (11) overlies a first oxide layer (12A), which overlies thesubstrate structure (10).

[0036] A silicon oxynitride layer (16) is formed on the oxide layer(12B). The silicon oxynitride layer (16) has a refractive index ofbetween about 1.85 and 2.35 and an extinction coefficient of between0.45 and 0.75 at a wavelength of 248 nanometers. The silicon oxynitridelayer preferably has a thickness of between about 130 Angstroms and 850Angstroms.

[0037] The silicon oxynitride layer (16) is preferably formed byreacting silane, nitric oxide and helium in a plasma at temperaturesbetween about 200° C. and 550° C., at a pressure of between about 3 torrand 8 torr, and at a power of between about 120 watts and 200 watts.

[0038] A photoresist layer (20) is formed over the silicon oxynitridelayer (16). The photoresist layer (20) has a thickness of between about3000 Angstroms and 8000 Angstroms.

[0039] The photoresist layer (20) is exposed to light energy at awavelength of between about 245 nanometers and 250 nanometers anddeveloped to form openings (25) in the photoresist layer (20).

[0040] In a preferred embodiment, the oxynitride layer (16), the nitridelayer (14) and the oxide layer (12B) are patterned through the openings(25) to form a contact opening.

[0041] Third Embodiment

[0042] In the third embodiment, a silicon oxynitride layer (16) isformed over a nitride layer (14) and a monocrystalline orpolycrystalline silicon layer (11), either with or without a tungstensilicide top layer, on a substrate structure (10), and patterned with aresolution of down to 0.12 μm.

[0043] The method begins by forming a nitride layer (14) on a siliconlayer (11) of a substrate. The nitride layer is formed using a LPCVDprocess and having a refractive index of between 2.28 and 2.32 and anextinction coefficient (k) of between about 0.015 and 0.025 at awavelength of 248 nanometers.

[0044] A silicon oxynitride layer (16) is formed on the nitride layer(14). The silicon oxynitride layer (16) has a refractive index ofbetween about 1.85 and 2.35 and an extinction coefficient of between0.45 and 0.75 at a wavelength of 248 nanometers. The silicon oxynitridelayer preferably has a thickness of between about 130 Angstroms and 850Angstroms.

[0045] The silicon oxynitride layer (16) is preferably formed byreacting silane, nitric oxide and helium in a plasma at temperaturesbetween about 200° C. and 550° C., at a pressure of between about 3 torrand 8 torr, and at a power of between about 120 watts and 200 watts.

[0046] A dielectric layer (18) is formed over the oxynitride layer (16)and planarized. the dielectric layer (18) is preferably composed ofdoped or undoped silicon glass as is known in the art.

[0047] A photoresist layer (20) is formed over the silicon oxynitridelayer (16). The photoresist layer (20) has a thickness of between about3000 Angstroms and 5000 Angstroms. The photoresist layer (20) is exposedto light energy at a wavelength of between about 245 nanometers and 250nanometers and developed.

[0048] In a preferred embodiment, the dielectric layer (18), theoxynitride layer (16), and the nitride layer (14) are patterned throughthe openings to form a contact opening.

[0049] While the invention has been particularly shown and describedwith reference to the preferred embodiments thereof, it will beunderstood by those skilled in the art that various changes in form anddetails may be made without departing from the spirit and scope of theinvention.

What is claimed is:
 1. A method of patterning semiconductor devices witha resolution down to 0.12 μm on a substrate structure comprising thesteps of: a. forming an oxide layer over a monocrystalline siliconsubstrate structure; b. forming a nitride layer on said oxide layer;said nitride layer having a refractive index of between 2.28 and 2.32 ata wavelength of 248 nm; c. forming a silicon oxynitride layer on saidnitride layer; said silicon oxynitride layer having a refractive indexof between about 1.85 and 2.35 at a wavelength of 248 nm, an extinctioncoefficient of between 0.45 and 0.75 at a wavelength of 248 nm, and athickness of between about 130 angstroms and 850 angstroms; d. forming aphotoresist layer over said silicon oxynitride layer; and e. exposingsaid photoresist at a wavelength of between about 245 nm and 250 nm;whereby during exposure at a wavelength of between 245 nm 250 nm, saidsilicon oxynitride layer provides a phase-cancel effect.
 2. The methodof claim 1 wherein said nitride layer has a thickness of between about1000 Angstroms and 2500 Angstroms and said oxide layer has a thicknessof between about 50 Angstroms and 300 Angstroms.
 3. The method of claim1 which further includes etching said oxynitride layer, said nitridelayer and said oxide layer to form a contact opening.
 4. The method ofclaim 1 wherein said photoresist layer has a thickness of between about3000 Angstroms and 8000 Angstroms.
 5. The method of claim 1 wherein saidoxide layer is formed using a LPCVD process; said nitride layer isformed using LPCVD; and said silicon oxynitride layer is formed byreacting silane, nitric oxide and helium in a plasma at temperaturesbetween about 200° C. and 550° C., at a pressure of between about 3 torrand 8 torr, and at a power of between about 120 watts and 200 watts. 6.A method of patterning semiconductor devices with a resolution down to0.12 μm on a substrate structure comprising the steps of: a. forming anoxide layer on a silicon layer overlying a substrate structure; saidoxide layer being composed of silicon glass; b. forming a siliconoxynitride layer on said oxide layer; said silicon oxynitride layerhaving a refractive index of between about 1.85 and 2.35 at a wavelengthof 248 nm, an extinction coefficient of between 0.45 and 0.75 at awavelength of 248 nm, and a thickness of between about 130 Angstroms and850 Angstroms; c. forming a photoresist layer over said siliconoxynitride layer; and d. exposing said photoresist layer at a wavelengthof between about 245 nm and 250 nm; whereby during exposure at awavelength of between 245 nm and 250 nm, said silicon oxynitride layerprovides a phase-cancel effect.
 7. The method of claim 6 wherein saidoxide layer is composed of undoped silicon glass, has a thickness ofbetween about 1000 Angstroms and 5000 Angstroms, has a refractive indexof between about 1.4 and 1.65, and is formed using an O₃— TEOS process.8. The method of claim 6 wherein said oxide layer is composed of borondoped silicon glass and has a thickness of between about 1000 Angstromsand 5000 Angstroms, has a refractive index of between about 1.4 and1.65, and is formed using an O₃— TEOS process.
 9. The method of claim 6wherein said oxide layer is composed of boron and phosphorous dopedsilicon glass and has a thickness of between about 1000 Angstroms and5000 Angstroms, has a refractive index of between about 1.4 and 1.65,and is formed using an O₃— TEOS process.
 10. The method of claim 6 whichfurther includes etching said oxynitride layer and said oxide layer toform a contact opening and removing said photoresist layer.
 11. Themethod of claim 6 wherein said photoresist layer has a thickness ofbetween about 3000 Angstroms and 8000 Angstroms.
 12. The method of claim6 wherein said silicon oxynitride layer is formed by reacting silane,nitric oxide and helium in a plasma at temperatures between about 200°C. and 550° C., at a pressure of between about 3 torr and 8 torr, and ata power of between about 120 watts and 200 watts.
 13. A method ofpatterning semiconductor devices with a resolution down to 0.12 μm on asubstrate structure comprising the steps of: a. forming a nitride layeron a silicon layer of a substrate structure; said nitride layer having arefractive index of between 2.28 and 2.32 at a wavelength of 248; b.forming a silicon oxynitride layer on said nitride layer; said siliconoxynitride layer having a refractive index of between about 1.85 and2.35 at a wavelength of 248 nm, an extinction coefficient of between0.45 and 0.75 at a wavelength of 248 nm, and a thickness of betweenabout 130 Angstroms and 850 Angstroms; c. forming a photoresist layerover said silicon oxynitride layer; and d. exposing said photoresist ata wavelength of between about 245 nm and 250 nm; whereby during exposureat a wavelength of between 245 nm and 250 nm, said silicon oxynitridelayer provides a phase-cancel effect.
 14. The method of claim 13 whereinsaid nitride layer has a thickness of between about 1000 Angstroms and2500 Angstroms.
 15. The method of claim 13 which further includesforming a dielectric layer over said silicon oxynitride layer andplanarizing said dielectric layer prior to forming said photoresistlayer; and etching said dielectric layer, said oxynitride layer and saidnitride layer to form a contact opening after exposing said photoresistlayer.
 16. The method of claim 13 wherein said photoresist layer has athickness of between about 3000 Angstroms and 8000 Angstroms.
 17. Themethod of claim 13 wherein said nitride layer is formed using a LPCVDprocess and said silicon oxynitride layer is formed by reacting silane,nitric oxide and helium in a plasma at temperatures between about 200°C. and 550° C., at a pressure of between about 3 torr and 8 torr, and ata power of between about 120 watts and 200 watts.